Robots Help to Bend Heavy-Metal Box Panels

December 1, 2007


 German fabricator BSC Bau-System-Center employs this two-robot automated press-brake cell to process blanks to 5 mm thick that weigh as much 480 kg and measure as large as 6.6 by 2 m. The line operates around the clock, six days a week.
After hitting upon the idea of industrializing the building trade with the aid of prefabricated steel box panels, Wolfgang Langer, managing director of German fabricator BSC Bau-System-Center, began to search for an integrated automation solution for production. The biggest challenge to automating: how to bend the heavy steel plates, which measure as long as 6 m and weigh as much as 480 kg. The firm found a solution in a team of two cooperating robots—Model KR 500 robots from Kuka Roboter GmbH—that move the heavy and awkward material in and out of a press brake.

BSC Bau-System-Center, based in Eisenhüttenstadt, Germany, reportedly is the world’s only industrial manufacturer of customized building structures made from specially bent, large-area steel box panels. The company employs 20, to supply ready-made precision-fit elements in a variety of shapes and sizes, in lengths to 6 m.

“Steel box panel technology can be used to industrialize the building trade,” explains Langer. “This system concept offers a great degree of planning flexibility and allows us to implement customer-specific solutions.”

Accurate to Within 0.1 mm

Unfortunately, Langer had to wait 16 years from his idea’s conception, in the early 1990s, to the development of a production system for the steel box panels. “The use of robots, with their payload capacity of 500 kg combined and with their ability to work together as a team, provided the breakthrough we needed,” Langer emphasizes. “Another important factor was the ability to integrate the robot controllers into the overall system program.”

The use of cooperating robots is based on Kuka’s RoboTeam technology, promising precise synchronization and geometrical coordination of all path motions and operations within the robot team. Process accuracy results from precision synchronization and the real-time exchange of the required data.

Each robot in the RoboTeam has its own standard controller. The robots communicate with each other over a high-speed local Ethernet network to coordinate their actions. One robot acts as the team leader.

Parallel to RoboTeam, Kuka developed a new programming philosophy. Here, it is not the motion of the individual robots that is programmed, but that of the workpiece.

High Uptime, Flexibility

The resulting production line processes blanks as thick as 5 mm and as large as 6.6 by 2 m. The line operates around the clock, six days a week. With only 20 days per year planned for maintenance and servicing of the robotic press-brake line, high equipment availability is essential. Offline programming of the robots helps here, as programming is uncoupled from manufacturing so that the robots can continue feeding the press brake in production while programmers develop new programs.

“Our requirements for the robots go beyond this, however,” says Langer. “One precondition for the production of the box panels is an angular and dimensional accuracy of up to 0.1 mm relative to the entire workpiece. Further, we require a cycle time of 8.5 min. to achieve the planned annual quantity of 400,000 sq. m of plate.

“The robots also must be very flexible,” continues Langer, “due to the varying lengths and widths of the finished panels.”

The KR 500 robots can be operated independently of the other machines in the overall system. This fact can be exploited for contract work.

 
Each of the four edges of the blank takes a two-step bend to 90 deg. Robot motion corresponds to the downward motion of the press-brake ram—when the ram reaches its lowest position, the robots also reach the end point of their motion paths.

Versatile Grippers

To begin production of a box panel, a gantry crane loads a coil of steel onto a coil lift truck at the head of the automated production line. This truck, running on a track, transfers steel strip weighing as much as 30 tons to an uncoiler. The strip is then processed by a straightening unit, and a laser system cuts holes, corner indentations for the folds, apertures for supply lines and other order-specific openings in the steel plate.

A roller conveyor then delivers the prepared plates to the two six-axis material-handling robots. Each plate is first positioned against a stop and then pushed into a defined position by pneumatic cylinders. Sensors monitor the process and if plate dimensions change, an operator enters the new values into the computer.

The robots generally grip all plates centrally. In the case of very wide workpieces, however, the operators can program an eccentric pickup position.

The two robots traverse a common linear unit to pick up a plate with their suction-cup grippers, mounted on end-of-arm fixtures that measure 2.6 m long by 1 m wide. The end effectors developed for this application each carry six different suction-cup modules; depending on the task, the system operator activates, via the controller, the appropriate gripper modules.

Complex, Counter-Directional Motions

It takes two robots to handle the plates, otherwise, the plates would sag. Langer, pointing to the robots as they rotate a plate in order to hold it in a defined position against the backgauges of the press brake, says, “Just take a look at these complex, counter-directional motions. They clearly show that cooperating robots were the only possible solution for this application.”

Each of the four edges of the blank takes a two-step bend to 90 deg. Robot motion corresponds to the downward motion of the press-brake ram—when the ram reaches its lowest position, the robots also reach the end point of their motion paths. After each bend, the robots set the plate down on a turntable, which rotates the plate through 90 or 180 deg. The setdown and pickup position on the turntable is programmed.

Upon completion of the bending process, the robots set the steel box panel down on a support, where a roller conveyor transports it for welding. MF


Information for this article supplied by Kuka Robotics Corp., Clinton Township, MI; 866/873-5852; www.kukarobotics.com.
Industry-Related Terms: Bending, Blank, Case, Corner, Grippers, LASER, Lines, Ram, Plate, Point
View Glossary of Metalforming Terms

 

See also: KUKA Robotics Corp.

Technologies: Pressroom Automation

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